This application makes reference to and claims all benefits accruing under 35 U.S.C. Section 119 from an application entitled, xe2x80x9cAlkaloid Halogen-Doped Sulfide Glasses for Opitical Amplifier and Fabricating Method thereof,xe2x80x9d filed in the Korean Industrial Property Office on Jul. 6, 2000 and there duly assigned Serial No. 2000-38691.
1. Field of the Invention
The present invention relates generally to sulfide glasses and a fabricating method thereof. More particularly, the present invention relates to sulfide glasses used as an optical amplifier and the fabricating method thereof.
2. Description of the Related Art
The following list of literature reference is indicative of the extensive research conducted in recent years in the field of sulfide-containing glasses.
 less than References greater than 
1. xe2x80x9cHigh-Gain Rare Earth Doped Fiber Amplifier Operating at 1.54 xcexcmxe2x80x9d, in Tech. Digest of Conference on Optical Fiber Communication, Reno Nevada (Optical Society of America. Washington, D.C.), W12, 167 (1987) by R. J. Mears, L. Leekie, I. M. Jauncey, and D. N. Payne.
2. xe2x80x9cAmplification and Lasing at 1350 nm in Neodymium Doped Fluorozirconate Fiberxe2x80x9d, Electron. Lett. 24, 438 (1988) by M. C. Brierley and C. A. Millar.
3. xe2x80x9cPr3+xe2x80x94doped Fluoride Fibre Amplifier Operating at 1.31 xcexcmxe2x80x9d, Opt. Lett. 16, 1747 (1991) by Y. Ohoshi, T. Kanamori, T. Kitagawa, S. Takahashi, E. Snitzer, and G. H. Sigel, Jr.
4. xe2x80x9cAmplification at 1.3 xcexcm in a Pr3+xe2x80x94Doped Single Mode Fluorozirconate Fibrexe2x80x9d, Electronics Letters vol. 27, no. 8, 628 (1991) by S. F. Carter, D. Szebesta, S. T. Davey, R. Wyatt, M. C. Brierley, and P. W. France.
5. xe2x80x9cPr3+: Laxe2x80x94Gaxe2x80x94S Glass: A Promising Material for 1.3 xcexcm Fiber Amplificationxe2x80x9d, in Tech. Digest of Topical Meeting Optical Amplifiers and their Applications. PDP5 (1992) by P. C. Becker, M. M. Broer, V. C. Lambrecht, A. J. Bruce, and C. Nykolak.
6. xe2x80x9cPr3+xe2x80x94Doped Gexe2x80x94Gaxe2x80x94S Glasses for 1.3 xcexcm Optical Fiber Amplifiersxe2x80x9d, J. Non-Cryst. Solids, 182, 257 (1995) by K. Wei, D. P. Macherwirth, J. Wenzel, E. Snitzer, and G. H. Sigel, Jr.
7. Spectroscopy and Quantum Efficiency of Halide-Modified Gallium-Lanthanium Sulfide Glasses Doped with Praseodymiumxe2x80x9d, J. Non-Cryst. Solids, 239, 176 (1998) by J. R. Hector, J. Wang, D. Brady, M. Kluth, D. W. Hewak, W. S. Brocklesby, and D. N. Payne.
In general, an optical communication system operates at the zero dispersion wavelength band, 1.31 xcexcm, and a minimum loss wavelength band, 1.5 xcexcm of silica glass, as an optical wave-guide material [See reference 1]. Particularly in the 1.31 xcexcm wavelength band, the rare-earth ions of Nd3+, Dy3+, and Pr3+exhibit fluorescence transition. Efforts have been made toward utilization of these rare-earth ions.
With reference to Nd3+, the central wavelength of fluorescence resulting from transition from the energy level of 4F3/2 to 4F13/2 is 1.35 xcexcm, which is different from the zero dispersion wavelength band of silica glass. Moreover, the probability of fluorescence emission at 1.31 xcexcm is only one fifth of the fluorescence emission probability at 0.89 xcexcm and 1.064 xcexcm that are simultaneously generated at 4F3/2. The gain at 1.31 xcexcm drops due to a strong, excited state absorption [See reference 2].
Dy3+produces fluorescence at 1.31 xcexcm across an induced emission area that is four times larger than Pr3+, and has a high branching ratio relative to other rare-earth elements. Despite these advantages, Dy3+has a very narrow energy difference, about 1800 cmxe2x88x921 between the fluorescence levels of 1.31 xcexcm, 4F11/2 or 6H9/2, and the nearest lower energy level 6H11/2s. Here, the resulting multiphonon relaxation leads to energy loss. Consequently, Dy3+has only 10% of the fluorescence lifetime of Pr3+, which are low fluorescence efficiency and a low gain coefficient needed for light amplification.
While Pr3+ induces fluorescence at 1.31 xcexcm utilizing transition 1G4 to 3H5 and has a much higher 1.31 xcexcm fluorescence transition probability than other fluorescence transition probabilities, it also has a narrow energy difference, 3000 cmxe2x88x921 between 1G4 and 3F4. Thus, when an oxide glass having a phonon energy of 800 cmxe2x88x921 or above is used as a base material, it is highly probable that the energy of Pr3+ ions excited to 1G4 experiences radiation-less transition due to the multiphonon relaxation, which results in the decrease of optical amplification efficiency. To solve the problem, a fluoride glass or a sulfide glass that has low phonon energy was suggested as a base material. However, the use of the fluoride glass as a base material can not produce high optical amplification efficiency because its quantum efficiency is very low, 4%. The sulfide glass as a base material is not effective in achieving high optical amplification efficiency due to its short fluorescence lifetime, 300 xcexcs at 1G4 [See references 3 to 7].
FIG. 1 illustrates the multiphonon relaxation of Pr3+ between energy levels, and the energy transfer between Pr3+ ion. The 1.31 xcexcm fluorescence lifetime and the optical amplification efficiency of Pr3+ at 1G4 are much influenced by radiation-less transition in which energy excited to 1G4 is consumed in a form other than light. The radiation-less transition refers to the multiphonon relaxation of phonon energy, as indicated reference character a, and the energy transfer between adjacent Pr3+ ions, as indicated by reference character b in FIG. 1. The multiphonon relaxation is a dominant factor that decreases the optical amplification efficiency.
The present invention provides alkali halide-doped sulfide glasses to be used as an optical amplifier and its fabricating method to extend fluorescence lifetime by eliminating the multiphonon relaxation, thus increasing the optical amplification efficiency of the optical amplifier.
The present invention can be achieved by providing alkali halide-doped sulfide glasses for an optical amplifier and a fabricating method thereof. An alkaloid halogen-doped sulfide glass is formed of silica doped with a Gexe2x80x94Gaxe2x80x94S three-component system, Pr3+, and an alkali halide. To fabricate alkali halide-doped sulfide glass for an optical amplifier, silica doped with Ge, Ga, S, Pr3+, and an alkali halide as a starting material is filled into a container. The container is sealed in a vacuum and the starting material in the container is fused by heating the container. The container is cooled and the starting material is sintered by heating the container at a glass transition temperature.
According to one aspect of the present invention, the Pr3+ and alkali halide-doped sulfide comprises a mixture of GeGaS and CsBr, expressed in terms of mole percent on the sulfide basis, and is selected from the group consisting of 90-92% (Ge0.25Ga0.10S0.65) and 8-10% (CsBr); 94.5-96.0% (Ge0.29Ga0.05S0.66) and 4-5.5% (CsBr); and, 84.2-85.25% (Ge0.18Ga0.18S0.64) and 14.75-15.75% (CsBr).
According to another aspect of the invention, the Pr3+ and alkali halide-doped sulfide glass comprises a mixture of GeGaS and KBr, expressed in terms of mole percent on the sulfide basis, and comprises 90.91% (Ge0.25Ga0.10S0.65) and 9.09% (KBr).
According to a further aspect of the invention, the Pr3+ and alkali halide-doped sulfide glass comprises a mixture of GeAsGaS and CsBr, expressed in terms of mole percent on the sulfide basis, and comprises 98% (Ge0.30As0.06Ga0.028S0.62) and 2%(CsBr).
Preferably, the alkali halide-doped is CsBr or Kbr.